That, and the fact the new XAML UX framework can only be used by AppX apps that run in the sandbox. “Normal”, otherwise unconstrained Win32 programs can’t use it.
As a user I personally prefer more powerful software and a more financially motivated developer; even when it makes buying more bespoke.
Last I checked, I had to assemble the above from disparate services, investigating each, integrating them, and paying for each, which doesn't seem like a productive use of my time or money.
Assembling from disparate sources will have more of an upfront cost but cost less per purchase. So it depends entirely on your sales volume.
Regarding your second point, interesting, seems like MAS is good to get started until the app reaches a certain volume.